.main {
    margin-top: 64px;
}
.course-nav {
    height: 54px;
    width: 100%;
    background: #f2f2f2;
    box-shadow: 0 4px 5px rgba(0, 0, 0, .1);
}
.course-nav .nav-container {
    width: 1170px;
    margin: 0 auto;
    overflow: hidden;
    line-height: 54px;
}
.course-nav .nav-container .title {
    float: left;
    color: #696969;
    font-size: 24px;
}
.course-nav .nav-container .nav-list {
    float: left;
    overflow: hidden;
    margin-left: 100px;
}
.course-nav .nav-container .nav-list li {
    float: left;
    margin-right: 40px;
}
.course-nav .nav-container .nav-list .active a {
    color: #212121;
}
.course-nav .nav-container .nav-list li a {
    color: #888;
}


.wrapper {
    margin: 0 auto;
    width: 1170px;
    margin-top: 20px;

}
.course-list {
    overflow: hidden;
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: space-between
}
.course-list li {
    width: 278px;
    height: 280px;
    float: left;
    background: #fff;
    margin-bottom: 20px;
}
.course-list li:hover {
    box-shadow: 0 4px 10px rgba(0,0,0,.1);
}
.course-list li .thumbnail {
    width: 100%;
    height: 158px;
}
.course-list li .thumbnail img{
    width: 100%;
    height: 100%;
}
.course-list li .course-info {
    width: 100%;
    height: 122px;
    padding: 16px;
    box-sizing: border-box;
    position: relative;
}
.course-list li .course-info .title-cu {
    color: #212121;
}
.course-list li .course-info .author-cu {
    margin-top: 10px;
    color: #878787;
    font-size: 14px;
}
.course-list li .course-info .price-cu {
    position: absolute;
    bottom: 16px;
    right: 16px;
}
.course-list li .course-info .price-cu .free{
    color: rgb(126,211,33);
}.course-list li .course-info .price-cu .pay{
    color: rgb(175,74,74);
}
